Traditionally, roof units such as roof windows, skylights and other more or less light transmissible roof penetrating structures provide natural lighting to a space situated immediately below or only a short unobstructed distance from the part of the roof, in which the roof unit is installed. For illuminating other spaces such as rooms situated further inwards and/or downwards with respect to the roof of the building, artificial lighting has been the dominating source of light.
For many reasons, natural lighting may be desirable in a room. In order to provide lighting or supplement artificial lighting of an inner room, roof window assemblies of the kind mentioned in the introduction have been suggested and are well known in the art. In such an assembly, a light conduit is led through the roof structure between the roof unit installed in the roof and a diffuser unit installed in the ceiling of an inner room. Light from the ambience is channelled through the light conduit into the inner room. The light conduit may e.g. be formed as a length of flexible hose, possibly reinforced by wire hoops, or rigid sections connected with each other to form the desired path of the light conduit between the roof unit and the diffuser unit. In order to ensure that as much natural lighting as possible is channelled from the outside to the inner room, the internal side of the light conduit is usually provided with a light reflective lining or coating, or the entire material of the light conduit is made from a light reflective material.
In some fields of application, ventilation of the inner room is desirable or even required, as is e.g. the case in a bathroom. In order to allow moist air to escape from the inner room and fresh air from the outside to enter the room, ventilation means leading from the room to the roof may be provided.
In its simplest form such ventilation means is in the form of apertures in the diffuser unit and the roof unit, respectively. Air is thus allowed to flow inside the light conduit itself. Examples of prior art making use of this type of arrangement are U.S. Pat. No. 5,435,780 and published international application No. WO 02/25032. However, problems of condensation may arise as the warm humid air from the inner room enters the light conduit and is transported in the direction of the roof unit. Furthermore, the apertures in the roof unit, although usually formed in concealed positions, entail a risk of entry of precipitation.
In order to alleviate the problems with condensation in the light conduit, one example of a solution is represented by U.S. Pat. No. 6,142,645, in which a separate venting duct is provided. The venting duct is coupled to the diffuser unit at the ceiling of the inner room and is led to an aperture in the roof adjacent the skylight itself. Although this design makes it possible to let moist air flow outside the light conduit, an additional aperture must be formed in the roof, which is not desirable from i.a. an aesthetic point of view.
A further development of this concept is known, in which a second tube surrounds a first tube constituting the light conduit. Ventilation is carried out in the space defined by the inner wall of the second tube and the outer wall of the first tube. Although this solution might be satisfactory in use, it is necessary to install the entire system simultaneously as subsequent installation of the second tube is, in most cases, impossible. Furthermore, ventilation is confined to the area adjacent the light conduit, as the inner end of the second tube necessarily ends at the inner end of the light conduit.
With this background it is an object of the present invention to provide a roof light system of the kind mentioned in the introduction, in which the risk of condensation is eliminated, which is at the same time easy to install, and by which a higher degree of flexibility with respect to ventilation conditions is achieved.
This and further objects are met by a roof light system of the kind mentioned in the introduction, which is furthermore characterized in that said at least one ventilation tube is separate from the light conduit, said second cross-section being detached from said first cross-section, and that said first end of the ventilation tube is connected with the roof unit and said second end is positioned at a distance from the diffuser unit.